1. Field of the Invention
The present invention relates generally to an automated analyzer and, more particularly, to an analyzer capable of automatically performing blood chemistry determinations and analyses of other biological and biochemical liquids and gases.
2. Description of the Prior Art
Various apparatus are presently available to make electrochemical measurements, such as potentiometric and polarographic measurements, on small liquid samples, which for practical purposes in the biological and biochemical field means sample volumes between 10 microliters and 1000 microliters. Examples of potentiometric measurements, which can be of interest to make in such small samples, are the determination of pH and PCO.sub.2, the latter being the partial pressure of carbon dioxide. An example of a polarographic measurement is the determination of PO.sub.2, the partial pressure of oxygen.
The determination of the parameters of pH, PCO.sub.2 and PO.sub.2, in so-called microvolumes of blood is most important in medicine. From the direct measurement of pH and PCO.sub.2 the determination of CO.sub.2 content, bicarbonate and buffer base can be readily obtained using the Hastings-Singer or similar nomograms. In addition, blood oxygen saturation can be determined quickly from the direct measurement of pH and PO.sub.2 and the use of oxygen disassociation curves or nomograms. These measurements are particularly useful to cardio-pulmonary specialists and have been a valuable aid in surgery, pulmonary function studies, cardiac catheterization, anesthesia studies and in clinical laboratories for determination of "acid-base" imbalance.
In view of the increasing importance in research and clinical medicine for making the aforementioned measurements, particularly with respect to microvolumes of blood, a need has arisen for rapid, reliable and economical instrumentation which would allow such analyses to be performed automatically. Presently available blood chemistry analyzers have several drawbacks, an important one being that the pH measuring electrode system is separate from the PCO.sub.2 and PO.sub.2 blood measuring systems so that a single sample must be divided and introduced into each system independently or sequentially. Moreover, the operation of presently available blood chemistry analyzers require considerable operator attention and technical skill. One particular blood chemistry analyzer is claimed to be fully automatic, but in actuality is semi-automatic inasmuch as the sample must be held manually in a syringe or other sealed container at the inlet port of the apparatus while a vacuum pump draws the sample through the apparatus for analysis. In addition, while means are provided for automatically circulating a wash solution through the major portion of the flow passages in the apparatus, the operator must hold a bottle of wash solution at the sample inlet port to assure that all sample will be cleaned from the inlet end of the sample passage to avoid any carryover of sample into the analysis cell from one test to another. The operator must also observe lights appearing on the instrument panel of the analyzer to determine when the sample and wash solution containers should be introduced to and withdrawn from the sample inlet port thus prohibiting the operator from performing other tasks in the laboratory. In addition, the pH electrode and the PCO.sub.2 and PO.sub.2 sensors must be calibrated separately since a buffer solution is utilized to calibrate the pH electrode and a humidified gas is utilized as the calibration media for the gas measuring sensors. In view of the foregoing, it can be appreciated that there is a need for a more automated apparatus for performing blood chemistry analyses, preferably one which will require virtually no operator attention and will overcome some if not all of the disadvantages discussed above in connection with the presently available systems. The purpose of the present invention is to provide such an apparatus.